Practical and efficient generation of electrical energy has been sought since the discovery of electricity. Hydroelectric, fossil fuel and nuclear generation plants and batteries have long been used to supply our electrical power needs. Power generation by use of fuel cells is a relatively recent development that is rapidly gaining acceptance for both commercial and residential applications. As compared with conventional fossil fuel burning powered sources, they are relatively clean and efficient. Fuel cells are electrochemical devices that efficiently convert a fuel's chemical energy directly to electrical energy. They chemically combine a fuel and oxidant without burning, thereby eliminating many inefficiencies and most pollution of traditional combustion power systems.
A fuel cell operates in principle much like a battery. However, unlike a battery, a fuel cell does not run down or require recharging. It will continue to produce energy in the form of electricity and heat as long as fuel is supplied to it. In general, a fuel cell consists of two electrodes (an anode and a cathode) sandwiched around an electrolyte. For example, for a PEM fuel cell, hydrogen and oxygen are passed over the anode and cathode electrodes respectively in a manner that generates a voltage between the electrodes, creating electricity and heat, and producing water as the primary byproduct. The hydrogen fuel is supplied to the anode of the fuel cell. Some consume hydrogen directly, while others use a fuel reformer to extract the hydrogen from, for example, a hydrocarbon fuel such as natural gas, methanol, ethanol, or gasoline. Oxygen enters the fuel cell at the cathode. The oxygen can be supplied in purified form or can come directly from atmospheric air.
The fuel cell uses a catalyst to cause the hydrogen atom to split into a proton and an electron, each of which takes a different path to the cathode. The protons pass through the electrolyte. The electrons create a useful electric current that can be used as an energy source, before returning to the anode where they are reunited with the hydrogen protons and the oxygen to form water.
Fuel cells are generally characterized by the electrolyte material which is sandwiched between the cathode and anode, and which serves as a bridge for ion exchange. There are five main known types of fuel cells. Alkaline fuel cells (AFCs) contain a liquid alkaline electrolyte and have been used primarily in space mission applications. Proton exchange membrane fuel cells (PEMFCs) contain a solid polymer electrolyte. Their low temperature operation, high power density with the ability to vary their output quickly to meet shifts in power demand make their use ideal for both mobile and stationary applications, such as powering vehicles or buildings. Phosphoric acid fuel cells (PAFCs) utilize a phosphoric acid electrolyte and are currently used for commercial power generation. Molten carbonate fuel cells (MCFCs) contain a carbonate salt electrolyte, which becomes molten at the operating temperature of about 650° C. Solid oxide fuel cells (SOFCs) use a ceramic electrolyte material and operate up to about 1000° C. Both the MCFCs and the SOFCs can use carbon monoxide as fuel.
Fuel cells have a vast range of potential applications. They can be used to produce electricity for homes, businesses and industries through stationary power plants. Fuel cells produce a direct current (dc) that must be inverted to alternating current for grid-connected applications or for use with most consumer products. However, future fuel cells could be operated in both grid-connected and non-grid-connected modes. For residential applications, smaller fuel cell power plants could be installed for the production of both heat and power. They could also be used to provide power to remote residential entities having no access to primary grid power, potentially eliminating the necessity of grid-connections.
In addition to the larger scale power production applications, fuel cells could replace batteries that power consumer electronic products such as laptop computers, cellular phones and the like and could even be micro-machined to provide power directly to computer chips. Another promising commercial application of fuel cells is their potential to replace the internal combustion engine in vehicle and transportation applications. The applications for fuel cells are virtually unlimited.
All of the known fuel cell configurations discussed above have a common need for oxygen as an integral ingredient for performing the cell's chemical process. Other power sources, such as internal combustion engines, including diesel engines, also have a need for oxygen. For most commercial applications it is desirable for such oxygen to be supplied directly from the atmospheric air. However, it is accepted that in today's world, all atmospheric air has some degree of contaminants present in it. Such contaminants can be relatively large such as loose debris, insects, tree blossoms or the like, or can be in the nature of small particulates suspended in the atmosphere such as dust, tree pollen, smog or smoke particulates. Chemical contaminants are also widely present in atmospheric air, whether as a result of man-made pollution or as those which naturally occur. Typical chemical contaminants might include volatile organic compounds such as aromatic hydrocarbons, methane, butane, propane and other hydrocarbons as well as ammonia, oxides of nitrogen, ozone, smog, oxides of sulfur, carbon monoxide, hydrogen sulfide, etc. Such contaminants may appear intentionally (such as in military environments or by terrorists) or unintentionally. Solution of the latter requirement becomes particularly acute when the fuel cell is used in a mobile application that subjects the fuel cell to many varied atmospheric conditions.
Since efficient fuel cell operation depends on a delicately balanced chemical reaction, contaminants in the air used by the cell can have a significant adverse effect on the cell's operation and, depending on their nature, can even cause the fuel cell to discontinue operation. It is important therefore, that the fuel cell system include a filtration system that is designed to eliminate harmful contaminants and one that enables the fuel cell to be used in a wide range of use environments. It is also important that other power generating equipment have a filtration system that is designed to eliminate harmful contaminants.
To obtain the amount of oxygen necessary for a fuel cell and other equipment to produce the desired energy output, it has been found desirable to pass the oxygen-bearing containing air through air movement equipment such as a compressor or fan located within the air flow stream supplied to the fuel cell or other equipment. Unfortunately, typical compressors produce significant undesirable and annoying noise levels. It is desirable, therefore, in a power generating system to reduce and to minimize the noise produced by and/or transmitted through the compressor and back into the environment. Since reduced system size is also typically desirable, it is preferable that the filtration and sound attenuation features of the system be physically reduced as small as possible and even preferably be combined within a single element or housing. The present invention addresses the above-identified needs and desires for an efficient and quiet system for use in a wide variety of applications, including fuel cell systems.
What is desired, therefore, is a power generator, such as a fuel cell, that functions within environments having a wide range of contaminants.